Deriving phenotypes for molecular genetic studies of substance use disorders: a family study approach

Although, family, twin, and adoption studies indicate that genes play a significant etiologic role in the development of substance use disorders (SUDs), the specific genes involved have been difficult to detect due, in part, to uncertainties about how best to define SUDs, the possibility of genetic heterogeneity and the variable phenotypic expression of SUD genotypes. The goal of the present work was to determine if phenotypes external to the diagnosis of SUD such as psychopathology and cognitive functioning would show evidence of utility as phenotypes for genetic studies of SUD. We did this by applying factor analysis to multiple measures collected from our family-study program and then determining if these factors were heritable and were co-familial with SUDs. We used data from families recruited into six contemporaneous studies of four psychiatric conditions in children and adults. We found evidence for two SUD related phenotypes. One was an index of Psychopathology and Psychosocial Impairment; the other was an index of school failure and cognitive dysfunction. Both factors showed evidence of heritability, longitudinal stability and familial association with Parental SUD but these findings were stronger for the index of school failure and cognitive dysfunction. Results provide some support for the idea that candidate SUD phenotypes such as psychopathology and cognitive functioning, which are external to the diagnostic criteria for SUDs, may be useful for genetic studies of SUD.